Method for controlling a continuous casting installation in the event of molten metal breakout

ABSTRACT

A method for controlling a continuous casting installation in the event of molten metal breakout wherein during the casting operation the light intensity at the secondary cooling zone of the continuously cast strand is monitored, changes in the light intensity with predetermined threshold values are compared and upon exceeding any such predetermined threshold values electrical signals are produced by means of which it is possible to control the continuous casting operation.

Nishikawa Jan. 22, 1974 [5 METHOD FOR CONTROLLING A 3,478,808 11/1969Adams .1 16 1/4 CONTINUOUS CASTING INSTALLATION IN 3,510,057 5/1970Werme 164/154 UX Appl. No.: 223,674

Foreign Application Priority Data Feb. 22, 1971 Japan 46-8843 U.S. Cl.164/4, 164/82 Int. Cl B2211 11/12 Field of Search 164/4, 82, 152-154References Cited UNITED STATES PATENTS 7/1940 Webster 164/278 X 3/1958Jones 164/4 OTHER PUBLICATIONS Marks Mechanical Engineers Handbook," 6thEdition, McGraw-Hill, N.Y., 1958, TJ151M37 1958 C9. Pages 16-17.

Primary ExaminerR. Spencer Annear Attorney, Agent, or FirmWerner W.Kleeman 5 7 ABSTRACT A method for controlling a continuous castinginstallation in the event of molten metal breakout wherein during thecasting operation the light intensity at the secondary cooling zone ofthe continuously cast strand is monitored, changes in the lightintensity with predetermined threshold values are compared and uponexceeding any such predetermined threshold values electrical signals areproduced by means of which it is possible to control the continuouscasting operation.

7 Claims, 3 Drawing Figures METHOD FOR CONTROLLING A CONTINUOUS CASTINGINSTALLATION IN THE EVENT or MOLTEN METAL BREAKOUT BACKGROUND OF THEINVENTION The present invention relates to a new and improved method ofcontrolling a continuous casting installation in the event ofmoltenmetal breakout, wherein the metal flowing out of the partiallysolidified strand produces a breakout signal by means of which thecontinuous casting installation can be controlled in accordance withrequirements.

Breakout of molten metal can arise during continuous casting with theliquid core or crater protruding past the end of the mold, especiallyduring the continuous casting of steel. When this phenomenon occursliquid metal flows out of the partially solidified strand through anopening in the thin peripheral skin or wall of the strand. There aremany different causes leading to breakout, such as slag inclusionsembedded in the peripheral wall of the strand, fissures, improper strandcooling, defects in the mold and so forth. Depending upon the nature ofthe breakout at the incipient stage thereof, as a general rule, verylittle metal per unit of time flows out. This stage of breakout isreferred to in the art as a starting or incipient breakout. Owing to themetal which flows out, but also because of the effects of the tensionalforces which prevail during strand withdrawal, the breakout opening inthe wall or skin of the strand which is small at the beginning of metalbreakout begins to increase in size so that eventually the outflowingquantity of metal per unit of time increases. Hence, it will be apparentthat the incipient or starting breakout with time leads to a breakouthaving a greater outflow quantity of metal per unit of time.

Breakouts not only'cause longer standstill or downtime of the continuouscasting installation or plant but they also impose expensive repair andreplacement work and costs. An operator at the mold can only firstascertain a breakout when the level of the molten metal in the moldquickly sinks, so that the above-mentioned starting or incipientbreakouts are not readily discernible by the operator because the levelof the molten metal bath does not visibly change. By the time that theoperator has finally ascertained a breakout, a considerable quantity ofmetal has alreadly flowed into the secondary cooling zone, resulting ininterruption in the casting operation and expensive repair andreplacement work. It has been found that such interruptions and repairscan be prevented if incipient breakouts can be ascertained and suitablemeasures initiated to cure same by freezing or solidifying the breakoutopening.

The prior art has already proposed a method for controlling a continuouscasting installation upon the occurrence of disturbances of the typewhich cause lowering of the metal bath level within the mold. Accordingto this state-of-the-art technique components, such as thermalindicators or fusible elements, arranged at the secondary cooling zone,generate signals for controlling the continuous casting installationupon the occurrence of a breakout. With this technique, however,

it is necessary to arrange such components as near as ever, whenpracticing this technique it should be recognized that owing to thearrangement of the components such tend to interfere with uniformspraying of the strand surfaces with the spray water. Of course it wouldbe possible to arrange these components externally of the spray patternin order to prevent such disturbances. But in so doing this would renderimpossible early detennination of the breakout. Furthermore, whenemploying cooling grids in the secondary cooling zone the use of thermalindicators or fusible elements is very expensive because owing to thegrid-like sub-division of the unsupported surfaces by an element only alimited surface can be monitored. Additionally this already knowntechnique does not permit any differentiation of a breakout as afunction of its size so that there can be immediately undertakenmeasures which are accommodated to the magnitude of such breakout.

SUMMARY OF THE INVENTION Hence, from what has been stated above, itshould be apparent that the art is still in need of an improved methodfor controlling a continuous casting installation in the event of abreakout which is not associated with the aforementioned drawbacks andlimitations of the state-of-the-art proposals. Therefore, a primaryobjective of the present invention is to provide a new and improvedmethod of controlling a continuous casting installation in the event ofmolten metal breakout which effectively and reliably fulfills theexisting need in the art and is not associated with the aforementioneddrawbacks and limitations of the heretofore advanced proposals.

Still a further significant object of the present invention relates to anew and improved method for controlling a continuous castinginstallation in the event of a breakout and which overcomes thepreviously discussed drawbacks of the state-of-the-art techniques andimportantly is capable of determining a breakout at the moment sucharises and then in accordance with its order of magnitude and topractically eliminate or reduce the damaging effects thereof.

Now, in order to implement these and still further objects of theinvention, which will become more readily apparent as the descriptionproceeds, the method aspects of this development propose measuring thelight intensity in the secondary cooling zone during the castingoperation by means of at least one photoelectric transmitter, comparingchanges in such light intensity with predetermined threshold valuesthereof, and obtaining signals by the comparison step which are thenused for control purposes.

When practicing this method of the invention it is possible to determinewithout delay the smallest incipient or commencing breakout at thestrand and to immediately initiate those measures necessary to cure suchdefects. Therefore it is equally possible to prevent shutdown of atravelling cast strand and avoid prolonged downtimes for repair andreplacement work at the casting installation. In the event that it is nolonger possible to repair the defect at the strand which caused thebreakout, even so only the smallest possible quantity of molten metal,typically steel, flows into the secondary cooling zone and thusthe'damage caused by such breakout is held to a minimum. Furthermore, itis possible to monitor a relatively large region of the slab pensed withthe uninterrupted monitoring of the bath level the automatic terminationof an incipient or starting breakout and the initiation of the requiredcorrective measures is of particular advantage.

The light intensity of the metal flowing out of the continuously caststrand during breakout is approximately proportional to the size ormagnitude of the breakout opening at the strand skin or wall. In thecase of a starting breakout the cooling chamber is only illuminated in aspark-like fashion by a number of metal or steel sprays. In order to beable to bring about freezing of the breakout opening at this stage, itis a further aspect of this invention that upon exceeding a firstthreshold value the metal feed is shutdown and the withdrawal of thecontinuously cast strand is briefly interrupted, thereafter the strandis moved further at a reduced withdrawal speed, and when the lightintensity drops below the first threshold value the casting operation isresumed with throttled metal feed.

If prior to exceeding a second threshold value freezing orre-solidiflcation of the breakout opening cannot be obtained and themeasured light intensity further increases, then, according to a stillfurther feature of this development, upon exceeding the second thresholdvalue, the low withdrawal speed is still further reduced and thequantity of infed cooling water is increased so as to promote the curingor repair of the defect. In continuous casting installations workingwith cooling plates or cooling grids it is particularly advantageous ifby virtue of the slow strand movement the starting or incipient breakoutis covered by a surface guide for the purpose of assisting freezing orre-solidification of the breakout.

In the case of breakouts of the type having large breakout openings inthe peripheral skin of the strand the third threshold value is exceededowing to the light emission of the outflowing metal jet as well as theglowing metal in the cooling compartment or chamber. The measures whichare then undertaken are directed towards protecting the equipment fromdamage as well as those concerning safety. Hence, according to a furtheraspect of this invention, the withdrawal of the strand is interrupted,an alarm signal produced for informing an operator about the conditionof the breakout and simultaneously the continuous casting installa' tionis switched over to manual control.

It is immaterial whether the light intensity during a breakout exceedsthe first, second and third threshold values in a rapid or slowsequence. In any event, and to the extent that there is no reduction inthe light intensity owing to freezing together of the breakout opening,the metal infeed into the mold is interrupted upon the occurrence of thefirst light beam produced by the starting or incipient breakout, so thateven if there is present a breakout which cannot be repaired only thesmallest quantity of metal can flow-out.

Upon repair of the breakout the light intensity again reduces so thatthe casting operation can be resumed. In order to protect the repairedskin or peripheral wall of the strand it is advantageous if, uponattaining the light intensity corresponding to normal operatingconditions, the installation is switched back in stages, that isstepwise, to the casting parameters which were present prior tobreakout.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be betterunderstood and objects other than those set forth above, will becomeapparent when consideration is given to the following detaileddescription thereof. Such description makes reference to the annexeddrawing wherein:

FIG. 1 is a vertical sectional view through a schematically illustratedcontinuous casting installation, depicting enough of the hardwarethereof necessary for understanding the inventive method;

FIG. 2 is a block circuit diagram of equipment employed in thecontinuous casting installation depicted in FIG. 1; and

FIG. 3 is a graph showing the course of the light intensity curves forthree different types of molten metal breakouts.

DESCRIPTION OF THE APPARATUS FOR PRACTICING TI-IE INVENTIVE METHODTurning now to the drawing it is to be understood that there has beenillustrated therein an exemplary arrangement of those components of thecontinuous casting installation necessary for clearly understanding theunderlying concepts of the inventive method disclosed herein.Considering therefore FIG. 1 more specifically 4 it is to be understoodthat an intermediate vessel or container 4 is equipped with a stopper 5which controls its outflow or discharge opening 5a. In a manner wellknown in the continuous casting art a partially solidifled continuouscast strand 7 is formed at the openended casting mold 6, this strand 7being supported at the secondary cooling zone 8 by rollers or rolls 9and cooled by spray water emanating from nozzles 10. Drive or withdrawalrolls 12 move the strand through the continuous casting installation inthe normal way. Photoelectric transmitter means, such as for instanceconventional photoelectric cells 14 are arranged at the secondarycooling zone 8 in such a manner that it is possible to measure a smallincrease in the light intensity caused by a starting or incipientbreakout. Depending upon the arrangement and dimensions of the spraycompartment or chamber 15 the photoelectric cells 14 could be arrangedinternally or externally of such spray compartment 15.

Considering now FIG. 2 there will be once again recognized thephotoelectric cells 14. Depending upon the prevailing light intensitythese photoelectric cells will deliver a corresponding signal or voltageto a conventional amplifier 40 which is provided at its input with astandard gain control or maximum value selector. The amplified signal orvoltage is delivered to any suitable threshold value indicators 41 to44, wherein the threshold value indicator 41 can be adjusted to a firstthreshold value, the threshold value indicator 42 to a second thresholdvalue, the threshold value indicator 43 to a third threshold value andthe threshold value indicator 44 to normal light intensity 22 (FIG. 3).The respective threshold values for the threshold value indicators 41,42 and 43 have been graphically depicted by reference characters 1, 2and 3 in FIG. 3. Any suitable control 49 may be provided for controllingthe process steps associated with the individual threshold values 1 to 3and the normal light intensity 22 with regard to the regulationmechanism 51 for controlling the intermediate container stopper 5, theroll withdrawal unit 12, the secondary cooling zone water control 53 andthe alarm mechanism 54 which may be acoustical or visual. Sincev thehardware for regulating the various components of the continuous castinginstallation just discussed are conventional and appear atstandardcontinuous casting plants it is unnecessary to discuss samefurther, particularly since the invention is not concerned with anyimprovements in such structure or the details thereof.

Now for the purpose of elucidating the invention there has beenillustrated in FIG. 3 a graph, along the ordinate of which there isplotted the light intensity and along the abscissa 21 of which there isplotted time. As already indicated abovethe first, second and thirdthreshold values have been plotted on this graph, 'and specifically thepredetermined light intensity of the first, second and third thresholdvalues have been respectively indicated by the horizontally extendinglines 1, 2 and 3. These light intensities can be determined most simplyby simulating breakouts of different orders of magnitude during normaloperation of the installation. For instance, in order to determine thelocation of the first threshold value 1 which, on the one hand, appearsduring a starting or incipient breakout, and on the other hand, to beable to distinguish such from a small breakout which is already flowing,a few drops of liquid steel are poured into the cooling compartment 15during casting and thus the light intensity is measured. By repeatingthis simulation of a starting breakout a number of times it is possibleto obtain very good average values of the light intensity for the lightemission of a small quantity of liquid metal during the operatingconditions prevailing in the cooling compartment 15. In the same way itis possible to determine the second threshold value 2 but with somewhatgreater quantity of liquid metal. The third threshold value 3 can beeasily determined outside of the cooling zone in that there is measuredthe light intensity of a quantity of metal which has flowed-out andwhich approximately corresponds to one-third to one-half of the moldcontent.

The curve 23 illustrates the course of the light intensity of a startingbreakout which has frozen or resolidified. During the time period 24 thelight intensity fluctuates in the cooling compartment 15 about a lowvalue which can be designated as the normal light intensity 22. At thepoint in 25 there begins a small breakout which at time point 26 reachesthe first threshold value 1. By means of the signal produced at thethreshold value transmitter 41 the delivery or feed of metal into themold 6 is blocked by the control 51 and the withdrawal of the strand isbriefly interrupted, that is to say for about up to approximately twentyseconds, by shutting-down the withdrawal unit 12. By virtue of the thuseliminated tension force at the skin or wall of the strand 7 it ispossible to cure a starting or incipient breakout caused by a crack orfissure. After this brief interruption, withdrawal of the strand at asmaller withdrawal speed continues, that is, at about one-half of thenormal strand withdrawal speed. Upon falling below the first thresholdvalue 1 at the time point 27 a throttled infeed of metal into the moldis initiated. After reaching the normal light intensity 22 at the timepoint 28 the casting installation switches back to normal operation instepwise fashion until reaching the casting parameters which prevailedprior to the breakout.

Continuing, it is to be understood that reference character 30represents a curve of the light intensity for a small breakout which canbe cured or repaired. At the point in time 26 the already describedmeasures are initiated. At the timepoint 31 the light intensity attainsthe value of the second threshold value 2. Consequently, the alreadyreduced withdrawal speed is still further reduced by about 50 percent.The strand is therefore now moved only with about 25 percent of thenormal withdrawal speed. Moreover at the time point 31 the quantity ofcooling water is increased to about 1.5 fold. By virtue of thesemeasures there is increased the possibility of curing or repairing smallbreakouts. Upon repairing the breakout the light intensity thereofreduces and the previously discussed measures for normalizing thecasting operation are again automatically initiated.

Finally, the light intensity curve 33 represents a breakout which cannotbe repaired or cured. At the point in time 34 the corresponding lightintensity curve 33 of such breakout exceeds the third threshold value 3.At the time points 26 and 31 the already abovediscussed measures havebeen initiated, without however bringing about a freezing together orresolidification of the breakout. At the time point 34 there istherefore now interrupted the withdrawal of the strand, an alarm signalis triggered and the continuous casting installation is switched-over tomanual operation.

While there is shown and described present preferred embodiments of theinvention, it is to be distinctly understood that the invention is notlimited thereto but may be otherwise variously'embodied and practicedwithin the scope of the following claims. Accordingly,

I claim:

1. A method of controlling a continuous casting installation in theevent of metal breakout, comprising the steps of continuously casting astrand, determining incipient metal breakout by monitoring during thecasting operation the light intensity at the secondary cooling zone forthe continuously cast strand at the location of such secondary coolingzone where cooling of the strand with water spray occurs, comparingchanges in the light intensity with predetermined threshold values,obtaining electrical signals in response to the light intensityexceeding a threshold value owing to incipient metal breakout, andcontrolling the continuous casting operation to counteract against metalbreakout in response to the electrical signals, said step of controllingthe continuous casting operation including:

a. at least briefly interrupting the feed of molten metal to the castingmold, and

thereafter continuing the casting operation at a reduced withdrawalspeed with throttled feed of the metal to the mold.

2. A method of controlling a continuous casting installation in theevent of metal breakout, comprising the steps of continuously casting astrand, monitoring during the casting operation the light intensity atthe secondary cooling zone for the continuously cast strand, comparingchanges in the light intensity with predetermined threshold values, uponexceeding a threshold value obtaining electrical signals by means ofwhich it is possible to control the continuous casting operation and tocounteract against metal breakout, wherein said predetermined thresholdvalues comprise a first threshold value and wherein upon exceeding saidfirst threshold value interrupting the feed of metal to the castingmold, briefly interrupting the withdrawal of the continuously caststrand, thereafter further moving the strand at a reduced withdrawalspeed, and when the light intensity falls below said first thresholdvalue continuing the casting operation with throttled feed of metal tothe mold.

3. The method as defined in claim 2, wherein said predeterminedthreshold values include a second threshold value, and upon exceedingsaid second threshold value further reducing the smaller withdrawalspeed and increasing the supply of water into the secondary coolingzone.

4. The method as defined in claim 3, wherein said predeterminedthreshold values include a third threshold value, and upon exceedingsaid third threshold value completely interrupting the withdrawal of thecontinuously cast strand, triggering an alarm signal and switching-overthe continuous casting installation to manual operation.

5. The method as defined in claim 2, further including the steps ofstepwise switching-back the continuous casting installation to operateat the casting parameters which prevailed prior to the breakout uponattaining a normal light intensity for the continuous castinginstallation which operation corresponds to the casting operation whichprevailed without the presence of molten metal breakout.

6. The method as defined in claim 1, further including the step of usingphotoelectric transmitter means for determining the light intensity atthe secondary cooling zone during the casting operation.

7. A method of monitoring a continuous casting installation for thepresence of breakout of molten metal from the continuously cast strand,comprising the steps of determining the light intensity prevailing at apredetermined zone of the continuous casting installation where coolingof the strand with water spray occurs, comparing the momentarilyprevailing light intensity with at least one predetermined thresholdvalue, producing an electrical control signal in response to the lightintensity exceeding a threshold value owing to incipient metal breakout,and controlling further operation of the continuous casting installationto act against metal breakout in response to said control signal, saidstep of controlling the continuous casting operation including:

a. at least briefly interrupting the feed of molten metal to the castingmold, and

b. thereafter continuing the casting operation at a reduced withdrawalspeed with throttled feed of the metal to the mold.

1. A method of controlling a continuous casting installation in theevent of metal breakout, comprising the steps of conTinuously casting astrand, determining incipient metal breakout by monitoring during thecasting operation the light intensity at the secondary cooling zone forthe continuously cast strand at the location of such secondary coolingzone where cooling of the strand with water spray occurs, comparingchanges in the light intensity with predetermined threshold values,obtaining electrical signals in response to the light intensityexceeding a threshold value owing to incipient metal breakout, andcontrolling the continuous casting operation to counteract against metalbreakout in response to the electrical signals, said step of controllingthe continuous casting operation including: a. at least brieflyinterrupting the feed of molten metal to the casting mold, andthereafter continuing the casting operation at a reduced withdrawalspeed with throttled feed of the metal to the mold.
 2. A method ofcontrolling a continuous casting installation in the event of metalbreakout, comprising the steps of continuously casting a strand,monitoring during the casting operation the light intensity at thesecondary cooling zone for the continuously cast strand, comparingchanges in the light intensity with predetermined threshold values, uponexceeding a threshold value obtaining electrical signals by means ofwhich it is possible to control the continuous casting operation and tocounteract against metal breakout, wherein said predetermined thresholdvalues comprise a first threshold value and wherein upon exceeding saidfirst threshold value interrupting the feed of metal to the castingmold, briefly interrupting the withdrawal of the continuously caststrand, thereafter further moving the strand at a reduced withdrawalspeed, and when the light intensity falls below said first thresholdvalue continuing the casting operation with throttled feed of metal tothe mold.
 3. The method as defined in claim 2, wherein saidpredetermined threshold values include a second threshold value, andupon exceeding said second threshold value further reducing the smallerwithdrawal speed and increasing the supply of water into the secondarycooling zone.
 4. The method as defined in claim 3, wherein saidpredetermined threshold values include a third threshold value, and uponexceeding said third threshold value completely interrupting thewithdrawal of the continuously cast strand, triggering an alarm signaland switching-over the continuous casting installation to manualoperation.
 5. The method as defined in claim 2, further including thesteps of stepwise switching-back the continuous casting installation tooperate at the casting parameters which prevailed prior to the breakoutupon attaining a normal light intensity for the continuous castinginstallation which operation corresponds to the casting operation whichprevailed without the presence of molten metal breakout.
 6. The methodas defined in claim 1, further including the step of using photoelectrictransmitter means for determining the light intensity at the secondarycooling zone during the casting operation.
 7. A method of monitoring acontinuous casting installation for the presence of breakout of moltenmetal from the continuously cast strand, comprising the steps ofdetermining the light intensity prevailing at a predetermined zone ofthe continuous casting installation where cooling of the strand withwater spray occurs, comparing the momentarily prevailing light intensitywith at least one predetermined threshold value, producing an electricalcontrol signal in response to the light intensity exceeding a thresholdvalue owing to incipient metal breakout, and controlling furtheroperation of the continuous casting installation to act against metalbreakout in response to said control signal, said step of controllingthe continuous casting operation including: a. at least brieflyinterrupting the feed of molten metal to the casting mold, and b.thereafter continuing the casting operation at a reduced withdrawalspeed with throttled feed of the metal to the mold.